This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 23 441.8, filed on May 21, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to an aircraft door structure with a door and a frame. The door has at least several load bearing beams spaced apart from each other and sandwiched between inner and outer door skins or claddings. Each beam end carries a stop member. When the door is closed the stop member bears against a stop element secured to the door frame surrounding a door opening in the aircraft body.
The pressure difference which arises in flight, between the passenger cabin and the outer atmosphere, results in pressure loads which need to be taken up by the door structure and transferred to the door frame which transmits these forces to the aircraft""s fuselage structure. The pressure loads applied at the door act in the direction of the pressure gradient, i.e. from the passenger cabin essentially in the direction to the outside of the fuselage. In order to take up these pressure loads the door structure comprises several load bearing beams spaced apart in different horizontal planes generally in the direction of the door width. These beams are connected to and sandwiched between the outside and inside skin or cladding of the door, thus providing rigidity to the door in the load direction of the applied pressure load.
U.S. Pat. No. 4,720,065 (Hamatami) discloses an outwardly or inwardly opening so-called plug-type aircraft door. A complicated latching and unlatching mechanism is required to operate the door. The conventional door of U.S. Pat. No. 4,720,065 also comprises elements for transferring the pressure loads to the frame and thus to the fuselage structure. For this purpose, each end of the load bearing beams has a stop member for cooperation with a corresponding stop element on the frame. Thus, the stop members at the level of the beam ends and the respective stop elements of the frame are provided in pairs. Normally a door comprises about six to eight stop members, depending on the number of beams cooperating with six to eight stop elements on the door frame.
When the door is closed, the stop members of the door bear against the stop elements of the frame in the direction of the pressure load. Thus each beam of the door is supported against the direction of the pressure load. If one or several of these stop members and elements break, a load redistribution occurs from the now unsupported beam end of the door to the stop members and elements still transferring load, whereby additional shearing and torsional loads act on the door structure. Such added loads can deform the door structure giving rise to the danger that the door""s pressure-sealing characteristics are diminished. Moreover, during flight the stop members and elements are subjected to dynamic loads, whereby not immediately noticeable cracks may occur in the stop members and/or in the stop elements or even failure of the stop members and/or elements may occur.
German Patent Publication DE-OS 2,907,550 (Bergman et al.) discloses a foldable insert door for an aircraft. The door and frame are provided with paired stop elements as shown in FIG. 1 of the present disclosure. The safety of such conventional doors leaves room for improvement, particularly with regard to the reliability of the seal in case one or more of the door stop pairs should fail.
German Patent Publication DE-OS 197 30 918 (Langlet) describes a locking mechanism for doors particularly aircraft doors. Mechanically or pneumatically or hydraulically driven spacer members are provided between the door and the door frame to assure a uniform load distribution around the door under all operating conditions whereby the door seals are protected.
In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination:
to avoid door stop failures in an aircraft door by improving the safety of the stops that support a closed door relative to the aircraft fuselage or body;
to reduce the weight of the door structure by providing redundant door stop features so that standard load conditions can be taken into account for determining door strength rather than maximum load conditions;
to reduce the need for conventionally required door stiffening features by providing redundant door stop features which have a door stiffening effect; and
to reduce production costs by providing door strength where needed and avoiding unnecessary reinforcements.
According to the invention the door and door frame construction for an aircraft comprises at least two pairs of load transmitting bearing surfaces arranged one behind the other in the load direction so that under normal operating conditions only one pair of the two pairs of bearing surfaces bears the load and the second or redundant pair becomes immediately effective in case of failure of an existing load transmission through the one pair of bearing surfaces. This second, immediately available load transmission transfers pressure loads from the door structure to the frame structure as a replacement of the normally effective load transmission, so that decompression is avoided. This second load transmission is made possible without large expenditure. Each pair of bearing surfaces comprises one bearing surface as part of the door structure and one bearing surface as part of the frame structure. A plurality of such double bearing surface pairs are preferably distributed around the door.
The term xe2x80x9carranged one behind the otherxe2x80x9d as used herein is intended to cover the in line arrangement of two pairs of load transmission surfaces and an arrangement in which the second pair is laterally displaced relative to the first pair and relative to the load direction just sufficient for the door to be opened without lifting.
According to one embodiment of the invention, one door stop bracket carries at least two bearing surfaces arranged one behind the other in the load direction. Similarly, one frame stop bracket carries at least two bearing surfaces also arranged one behind the other in the load direction. Preferably, each stop bracket comprises at least two bracket arms which provide the bearing surfaces.
According to another embodiment each bearing surface is part of its own separate door stop bracket or its own separate frame stop bracket. These separate brackets are individually secured to the door or to the frame respectively or may be integral parts of the respective door or frame. This feature of making the brackets integral parts of the door or frame applies to any brackets forming one or more bearing surfaces.
The invention makes it possible to increase safety with little effort and expense. Based on the invention, only the standard load conditions must be taken into account when calculating the strength and dimensions of the door. The heretofore additionally necessary door stiffeners no longer need to be part of the construction criteria for the door structure, whereby a significant weight reduction is achieved even if the stop brackets are heavier because the remaining door structure is lighter than heretofore, which also saves costs.